The processes and properties of the Higgs boson are the most recent and exciting new frontier in exploring fundamental physics at the smallest distance scales.
Today, the measured decays of the Higgs boson have been shown to agree well with the corresponding standard theory predictions at the current ~15% experimental precision. New results have been presented on the search for Higgs boson decays to invisible particles, which could for example constitute cosmological dark matter. An upper bound has also been set on the Higgs boson lifetime.
LHC measurements of the self-interactions among the electroweak gauge bosons have for the first time matched or surpassed the precision of all previous experiments and entered completely new territory in the corresponding tests of the standard electroweak theory. Similarly good agreement was observed in measurements of electroweak gauge boson production associated with hadronic jets, presented for the first time also at the highest LHC collision energies. This was reflected in the good overall agreement presented between standard theory predictions and combined electroweak and Higgs boson measurements.
Although the neutrinos are one of the most abundant fundamental particles their fundamental properties, like for example their masses, and whether or not there exist new types of neutrinos in addition to the three known types, are not known at all. The experiments utilising the solar, atmospheric, reactor neutrinos and neutrinos produced by particle accelerators have precisely measured the mass differences between different neutrinos and all parameters that determine the probabilities for one neutrino to transform to another one. The absolute masses are still not known but experimental prospects for measuring them are good. Experiments are in recent years focusing as well on measurements of possible differences between properties of neutrinos and anti-neutrinos. No differences were observed so far.
Yesterday, a dedicated presentation of the observation of new class of particles that consist of five quarks (known as pentaquarks) was given. Today, properties of several particles that were discovered in last couple of years and that belong to an another exotic class of particles consisting of four quarks (known as tetraquarks), were reviewed. The number of constituent quarks makes tetraquakrs and pentaquarks very special and may help us to better understand the ordinary matter, the protons and neutrons from which we’re all made of.
On the theory front, significant advances have been presented in the precision of predictions available for high energy processes at the LHC. While the leading strong-interaction corrections have been already fully automated, and several processes have been calculated up to second order, first results have been presented including up to third order quantum corrections due to strong interactions for the important process of Higgs boson production at the LHC.
Numerical, nonperturbative approaches to the strong interactions using discretization of space and time have also made significant advances and new results have been presented which improve our knowledge of the spectra and composition of strongly bound (hadronic) particles and allow for stringent tests of the standard theory of quark flavor transitions and quark – antiquark asymmetries.
Finally, recent intriguing advances in understand of quantum theories in lower dimensional spaces have been presented which suggest deep connections between some phenomena in complex condensed matter systems and the revolutionary possibility that all the elementary particles, including massless quanta of light (photons), are actually composite and thus not fundamental.